Numerical Analysis of Hydrogen Mild Combustion

Five hydrogen-oxygen combustion mechanisms were analyzed and compared on the basis of experimental ignition delay time data from shock-tube studies available in the literature. Stoichiometric and lean hydro- gen/air combustion were considered, as well as Mild Combustion conditions in the presence of different amounts of steam. The temperature varied between 900 and 1300 K, and pressure ranged from 0.1 to 0.9 MPa. Since deviations in almost all the analyzed conditions occurred, a sensitivity analysis was conducted to characterize the most influential reactions under the various initial conditions. In order to improve the numerical results, the reaction rate constants of the reaction HO2 + H = H2O2 + H2 were varied, as well as the third body efficiency of water in the breaking reaction H + O2 + M = HO2 + M. Although these variations did not lead to the identification of new kinetic constants, they clearly showed significant changes in the prediction of the ignition delay time. These results showed that the oxidation process is very sensitive to the reaction HO2 + H = H2O2 + H2 for low temperature values, as well as to the third body efficiency of the steam for higher temperatures.